1. Technical Field
The present invention relates to a method for one-pot synthesis of ionic liquid with fluoroalkyl group, more particularly to a method for one-pot synthesis of ionic liquid with fluoroalkyl group represented by the following Chemical Formula 1 by adding and reacting a nitrogen-containing compound, a Brønsted acid of the formula YH and a fluoroolefin compound of the formula CFR1═CR2R3 in a single reactor:

wherein
represents a nitrogen-containing compound; Y− represents an anion of the Brønsted acid; and R1, R2 and R3, which may be same or different, represent hydrogen, fluorine, C1-C10 alkyl or C1-C10 fluoroalkyl having from 1 to 23 fluorine atoms.
2. Background Art
An ionic liquid is a salt compound consisting of an organic cation and an anion. While salt compounds melt at relatively high temperature of 800° C. or above in general, ionic liquids exist as liquid even at relatively low temperature of 100° C. or below. In general, an ionic liquid is non-volatile, not-toxic, non-flammable and thermally stable, and has a good ion conductivity. Therefore, it is applied to various chemical areas, including a green solvent, a solvent for a catalyst, a separation medium or electrolyte, a solvent for hardly soluble materials such as cellulose, a storage medium for a toxic gas, or the like. Further, because the physical and chemical properties of ionic liquids can be tuned by changing the structure of the cation and the anion constituting the ionic liquid, an ionic liquid that is optimized for a particular application can be synthesized easily. Thus, it is commonly called as “designer solvent.” Typical examples of the ionic liquid are compounds consisting of a nitrogen-containing cation and an anion such as halogen like Cl−, Br− and I−, BF4−, PF6−, (CF3SO)2N−, CF3SO3−, MeSO3−, NO3−, CF3CO2−, CH3CO2−, etc. The nitrogen-containing cation constituting an ionic liquid may be quaternary ammonium, pyrrolidium, pyrrolium, imidazolium, pyrazolium, triazolium, pyridinium, pyridazinium, pyrimidinium, and the like.
The most common method of preparing an ionic liquid [Inorg. Chem. 1996, 35, 1168] is to react an imidazole compound with an alkyl halide (R2—X) to prepare an ionic compound, imidazolium halide, and then exchange the anion with a wanted anion (Y−) using a metal salt (MY) containing the anion, as shown in the following Scheme 1.

In Scheme 1, R1 and R2 independently represents hydrogen or alkyl; X represents halogen; M represents alkali metal; and Y represents Cl−, Br−, I−, BF4−, PF6−, (CF3SO)2N−, CF3SO3−, CH3SO3−, NO2−, NO3−, CF3CO2− or CH3CO2−.
The preparation method according to Scheme 1 consists of at least two steps, excluding the step of preparing the halogen anion containing compound. In addition, a step of removing the reaction byproduct, metal halide (MX), is required. Further, because the final product, the ionic liquid, dissolves the metal halide, it is almost impossible to completely remove the metal halide.
Recently, ionic liquid with fluoroalkyl group bonded to nitrogen-containing cation, as represented by Chemical Formula 1, has been developed. The ionic liquid with fluoroalkyl group represented by Chemical Formula 1 has many fluorine atoms in the molecule. Because fluorine is the most electronegative element, the liquid has distinct physical and chemical properties, including solubility and potential window, which is different from those of ionic liquids with hydrocarbon-based alkyl group. The ionic liquid with fluoroalkyl group represented by Chemical Formula 1 can be prepared by the multi-step process as described in Scheme 1. That is, after reacting imidazole with fluoroalkyl halide to obtain imidazolium halide with fluoroalkyl group, the wanted ionic liquid with fluoroalkyl group can be attained by exchanging the anion using a metal salt (MY) containing Y− anion.
However, as mentioned above, this preparation method is composed of two or more steps in order to obtain the ionic liquid with fluoroalkyl group, and requires the process for removing the reaction byproduct metal halide (MX). Further, because the final product, which is an ionic liquid, dissolves the metal halide, it is almost impossible to completely remove the metal halide. Besides, highly reactive fluoroalkyl iodide, which is used as alkylation reagent, is expensive and discolored easily upon exposure to air or light. This affects the color of the final product.
Recently, a method of synthesizing 1-(1,1,2,2-tetrafluoroethyl)imidazole by reacting a fluoroolefin compound such as tetrafluoroethylene (CF2═CF2) with imidazole has been proposed [WO 2007/074632; J. Fluorine Chem. 125 (2004) 1465; J. Fluorine Chem. 126 (2005) 669]. However, this method requires a further alkylation, and anion exchange step to introduce anions other than halide.